pub fn odd_fibnacci_sum(threshold: u32) -> u32 {
    let mut c1 = 0;
    let mut c2 = 1;
    let mut sum = 0;
    while c2 < threshold {
        if c2 % 2 == 1 {
            sum += c2;
        }
        let tmp = c2;
        c2 = tmp + c1;
        c1 = tmp;
    }
    sum
}
